Cathemerality and lunar periodicity of activity rhythms in owl monkeys of the Argentinian Chaco

Time-Dependent Effects of Dim Light at Night on Re-Entrainment and Masking of Hamster Activity Rhythms

Bright light has been established as the most ubiquitous environmental cue that entrains circadian timing systems under natural conditions. Light equivalent in intensity to moonlight (<1 lux), however, also strongly modulates circadian function in a number of entrainment paradigms. For example, compared to completely dark nights, dim nighttime illumination accelerated re-entrainment of hamster activity rhythms to 4-hour phase advances and delays of an otherwise standard laboratory photocycle. The purpose of this study was to determine if a sensitive period existed in the night during which dim illumination had a robust influence on speed of re-entrainment. Male Siberian hamsters were either exposed to dim light throughout the night, for half of the night, or not at all. Compared to dark nights, dim illumination throughout the entire night decreased by 29% the time for the midpoint of the active phase to re-entrain to a 4-hour phase advance and by 26% for a 4-hour delay. Acceleration of advances and delays were also achieved with 5 hours of dim light per night, but effects depended on whether dim light was present in the first half, second half, or first and last quarters of the night. Both during phase shifting and steady-state entrainment, partially lit nights also produced strong positive and negative masking effects, as well as entrainment aftereffects in constant darkness. Thus, even in the presence of a strong zeitgeber, light that might be encountered under a natural nighttime sky potently modulates the circadian timing system of hamsters.

Effects of meteorology, astronomical variables, location and human disturbance on the singing apes: Hylobates albibarbis

Gibbons are characterized by their species-specific calls. The frequency of singing is known to be affected by rainfall, with singing occurring less in the wet season. I investigate the hypothesis that gibbon singing is also affected by the natural light-dark cycle, and by the changing light intensity and air quality resulting from the smoke haze which blankets the Indonesian island of Borneo on a yearly basis. I compare three singing variables-onset of singing, average duration of singing bout and number of female great calls produced during the dry season of 2006 when there was no smoke haze (June-August) and when there was smoke haze present (September-November). I present evidence which indicates that the changes in singing behavior are affected by changes in rainfall and smoke intensity but not by other meteorological factors (i.e. wind and light intensity) or changing astronomical cues (light intensity, month, time of sunrise, time of moonrise, nocturnal illumination index, day length and night length). The possible long-term effects of this on gibbon behavior and territoriality are discussed. The need to carry out more research on the long-term effects of the smoke haze on wildlife behavior and possible solutions to the problem are discussed.

Sex, age, and family differences in the chemical composition of owl monkey (Aotus nancymaae) subcaudal scent secretions

Numerous behavioral studies have shown that animals use olfactory cues as inbreeding avoidance or kin avoidance mechanisms, implying that scent is unique to families. However, few studies have analyzed the chemical profile of a scent and ascertained the messages that are conveyed in scent secretions. Owl monkeys (Aotus nancymaae) are socially monogamous primates that utilize scent when interacting with foreign conspecifics. This suggests there is a difference in the chemical composition of scent marks. We chemically analyzed sub-caudal gland samples from three families of captive owl monkeys (Aotus nancymaae). Samples were analyzed by capillary GC-MS and relative retention time and fragment pattern was compared with known standards. Gland samples were high in large plant-based shikikate metabolites and fatty ketones; alcohols, acids, and acetates were virtually absent. Gender, age, and family could be reliably classified using discriminant analysis (92.9, 100, and 100%, respectively). Female scent profiles were greater in concentration of aromatic plant metabolites, possibly the result of a different diet or physiological differences in female metabolism as compared to male. Offspring of adult age still living in their natal group showed a less complex chemical profile than their parents. Finally, each family had its own unique and complex chemical profile. The presence of family scent may play a role in mediating social interactions.

Food transfers to young and mates in wild owl monkeys (Aotus azarai)

Accounts of food sharing within natural populations of mammals have focused on transfers to offspring or transfers of food items that are difficult to obtain (such as meat). Five groups of socially monogamous owl monkeys (Aotus azarai azarai) in Formosa, Argentina were observed during 107 hr to determine the pattern of food sharing under natural conditions. There were a total of 42 social interactions involving food with food being transferred on eight occasions. Adult males transferred food to young more often than did adult females. All types of food that were readily obtained and eaten by all age/sex classes were transferred to young. Adult females also transferred food to their mates. This type of food sharing is very rare among animals and may have social benefits specific to monogamous mammals with paternal care.

Exploring the role of vision in social foraging: what happens to group size, vigilance, spacing, aggression and habitat use in birds and mammals that forage at night?

I examined the role of vision in social foraging by contrasting group size, vigilance, spacing, aggression and habitat use between day and night in many species of birds and mammals. The literature review revealed that the rate of predation/disturbance was often reduced at night while food was considered more available. Social foraging at night was prevalent in many species suggesting that low light levels at night are not sufficient to prevent the formation and cohesion of animal groups. Group sizes were similar or larger at night than during the day in more than half the bird populations and in the majority of mammal populations. Factors such as calls, feeding noises or smells may contribute to the formation and cohesion of groups at night. Larger numbers of foragers at night may also facilitate the aggregation of more foragers. Vigilance levels were usually lower at night perhaps as a response to the lower predation risk or to the decreased value of scanning for predators that are difficult to locate. Low light levels may also make visual cues that promote aggression less conspicuous, which may be a factor in the lower levels of aggression documented at night. Spacing varied as a function of time of day in response to changes in foraging mode or food availability. Habitats that are avoided during the day were often used at night. Foraging at night presents birds and mammals with a new set of constraints that influence group size, time budgeting and habitat use.

Adult male replacement and subsequent infant care by male and siblings in socially monogamous owl monkeys (Aotus azarai)

Owl monkeys (Aotus azarai) are small, territorial, socially monogamous primates that show intense infant care by the adult male in the group. It has been hypothesized that male care may be adaptive because it increases offspring survival and/or reduces the metabolic costs to the female of raising the offspring. Alternatively, males may provide care even when they are not related to the infants to increase future reproductive opportunities. We describe changes in infant care patterns that took place after the eviction of the resident male by a solitary male in an owl monkey population in the Argentinean Chaco. The resident male and mother provided all infant care during the first month of life of the infant, until the male was evicted. During the three-day male replacement event, care of the infant was shared among the mother, a four-year-old sister, and a one-year-old brother. The new male began contributing to infant care soon after entering the group, carrying, and interacting socially with the infant in much the same way as any male regularly does. However, despite receiving biparental care from both the original and new resident males, the infant disappeared at the age of four months and was presumed dead. These are the first reports of care by sibling and by non-putative fathers in wild owl monkeys. Given the significant amount of time that new pairs of owl monkeys spend before reproducing, it is possible that male care in owl monkeys functions as mating effort as much as or more than parenting effort.

Mutational changes in S-cone opsin genes common to both nocturnal and cathemeral Aotus monkeys

Aotus is a platyrrhine primate that has been classically considered to be nocturnal. Earlier research revealed that this animal lacks a color vision capacity because, unlike all other platyrrhine monkeys, Aotus has a defect in the opsin gene that is required to produce short-wavelength sensitive (S) cone photopigment. Consequently, Aotus retains only a single type of cone photopigment. Other mammals have since been found to show similar losses and it has often been speculated that such change is in some fashion tied to nocturnality. Although most species of Aotus are indeed nocturnal, recent observations show that Aotus azarai, an owl monkey species native to portions of Argentina and Paraguay, displays a cathemeral activity pattern being active during daylight hours as frequently as during nighttime hours. We have sequenced portions of the S-cone opsin gene in A. azarai and Aotus nancymaae, the latter a typically nocturnal species. The S-cone opsin genes in both species contain the same fatal defects earlier detected for Aotus trivirgatus. On the basis of the phylogenetic relationships of these three species these results imply that Aotus must have lost a capacity for color vision early in its history and they also suggest that the absence of color vision is not compulsively linked to a nocturnal lifestyle.

Moonlight shifts the endogenous clock of Drosophila melanogaster

The ability to be synchronized by light-dark cycles is a fundamental property of circadian clocks. Although there are indications that circadian clocks are extremely light-sensitive and that they can be set by the low irradiances that occur at dawn and dusk, this has not been shown on the cellular level. Here, we demonstrate that a subset of Drosophila's pacemaker neurons responds to nocturnal dim light. At a nighttime illumination comparable to quarter-moonlight intensity, the flies increase activity levels and shift their typical morning and evening activity peaks into the night. In parallel, clock protein levels are reduced, and clock protein rhythms shift in opposed direction in subsets of the previously identified morning and evening pacemaker cells. No effect was observed on the peripheral clock in the eye. Our results demonstrate that the neurons driving rhythmic behavior are extremely light-sensitive and capable of shifting activity in response to the very low light intensities that regularly occur in nature. This sensitivity may be instrumental in adaptation to different photoperiods, as was proposed by the morning and evening oscillator model of Pittendrigh and Daan. We also show that this adaptation depends on retinal input but is independent of cryptochrome.

A re-evaluation of the role of vision in the activity and communication of nocturnal primates

This paper examines the importance of vision in the lives of nocturnal primates in comparison to diurnal and cathemeral species. Vision is the major sense in all primates and there is evidence that the eyesight of nocturnal species is more acute and variable than has previously been recognized. Case studies of the behaviour of a galago and a loris in open woodland habitats in relation to ambient light show that Galago moholi males are more likely to travel between clumps of vegetation along the ground when the moon is up, and during periods of twilight, whereas they retreat to more continuous vegetation and travel less when the moon sets. This is interpreted as a strategy for avoiding predators that hunt on the ground when it is dark. The travel distances of Loris lydekkerianus are not affected by moonlight but this species reduces its choice of food items from more mobile prey to mainly ants when the moon sets, indicating the importance of light when searching for high-energy supplements to its staple diet. Evidence is presented for the first time to indicate key aspects of nocturnal vision that would benefit from further research. It is suggested that the light and dark facial markings of many species convey information about species and individual identity when animals approach each other at night. Differences in the colour of the reflective eye-shine, and behavioural responses displayed when exposed to white torchlight, point to different kinds of nocturnal vision that are suited to each niche, including the possibility of some degree of colour discrimination. The ability of even specialist nocturnal species to see well in broad daylight demonstrates an inherent flexibility that would enable movement into diurnal niches. The major differences in the sensitivity and perceptual anatomy of diurnal lemurs compared to diurnal anthropoids, and the emergence of cathemerality in lemurs, is interpreted as a reflection of evolution from different ancestral stocks in very different ecosystems, and not a recent shift towards diurnality due to human disturbance.

Influence of abiotic factors on cathemeral activity: the case of Eulemur fulvus collaris in the littoral forest of Madagascar

The role environmental factors play in influencing circadian rhythms in natural habitats is still poorly described in primates, especially for those taxa with an activity cycle extended over the 24-hour cycle. In this paper, we elucidate the importance of abiotic factors in entraining the activity of cathemeral primates, focussing on results from a long-term study of Eulemur fulvus collaris (collared brown lemur) in south-eastern Malagasy littoral forest. Two groups of lemurs were followed for 60 whole-day and 59 whole-night observation periods over 14 months. Diurnal and nocturnal observations were equally distributed among moon phases and seasons. Temperature and humidity were recorded hourly by automatic data loggers. The littoral forest has a climatic environment where rainfall and humidity are uncorrelated with temperature and photoperiod. Diurnal and nocturnal activity varied seasonally, with the former increasing significantly with extended day length and the latter increasing significantly with shortened day length. Dusk seemed to act as a primary zeitgeber for these lemurs, coordinating the onset of evening activity throughout the entire year. Lunar phase and the nocturnal luminosity index correlated positively with the duration of nocturnal activity and negatively with the length of diurnal activity. Temperature was positively associated with diurnal activity but did not seem to influence lemur rhythms at night. Finally, lemur nocturnal activity significantly decreased when levels of humidity and rainfall were high. Cathemeral biorhythm is triggered by zeitgebers and influenced by masking factors. The activity of collared brown lemurs appears to be seasonally influenced by photoperiod and directly modulated by nocturnal ambient luminosity. These results are discussed by comparing data from other cathemeral species living in various climatic situations.

Photic entrainment and masking of prosimian circadian rhythms (Otolemur garnettii, Primates)

Besides rods the retina of the nocturnal greater bushbaby, genus Otolemur, also contains small cones which, however, do not allow color vision. In order to find out whether these cones might be involved in circadian photoreception in the Garnet's galago Otolemur garnettii we determined the threshold for photic entrainment. Activity recordings revealed a short circadian period of 22.6+/-0.7 h subjected to pronounced long-lasting aftereffects. The animals had a relatively high threshold for photic entrainment at about 3-30 lux. This indicates that the cones and/or other, as yet unidentified photoreceptive retinal cells may be involved in circadian photoreception. The galagos' threshold for photic entrainment also depended on the luminosity during the dark phase of the light dark cycles. Results furthermore showed that in Otolemur aftereffects may play a crucial role for circadian entrainment. Light time luminosities just below the individuals' threshold for photic entrainment strongly inhibited the galagos' locomotor activity and, thus, produced pronounced negative masking effects on their free-running circadian activity rhythm. From this it may be inferred that masking direct effects of light are not induced or mediated via the circadian system, i.e. via the circadian pacemaker in the hypothalamic suprachiasmatic nuclei, but at a higher central nervous integrational stage.

The Evolution of Cathemerality in Primates and Other Mammals: A Comparative and Chronoecological Approach

Non-primate mammalian activity cycles are highly variable across and within taxonomic groups. In contrast, the order Primates has historically been recognized as displaying a diurnal-nocturnal dichotomy that mapped, for the most part, onto the taxonomic division between haplorhines and strepsirhines. However, it has become clear over the past two decades that activity cycles in primates are not quite so clear cut. Some primate species--like many large herbivorous mammals, mustelids, microtine rodents, and shrews--exhibit activity both at night and during the day. This activity pattern is often polyphasic or ultradian (several short activity bouts per 24-hour period), in contrast to the generally monophasic pattern (one long bout of activity per 24-hour period) observed in diurnal and nocturnal mammals. Alternatively, it can vary on a seasonal basis, with nocturnal activity exhibited during one season, and diurnal activity during the other season. The term now generally employed to describe the exploitation of both diurnal and nocturnal phases in primates is 'cathemeral'. Cathemerality has been documented in one haplorhine, the owl monkey, Aotus azarai, in the Paraguayan and Argentinian Chaco and in several Malagasy strepsirhines, including Eulemur spp., Hapalemur sp. and Lemur catta. In this paper, we review patterns of day-night activity in primates and other mammals and investigate the potential ecological and physiological bases underlying such 24-hour activity. Secondly, we will consider the role of cathemerality in primate evolution.

Chronobiological Background to Cathemerality: Circadian Rhythms in Eulemur fulvus albifrons (Prosimii) and Aotus azarai boliviensis (Anthropoidea)

Cathemeral activity, in which the animals' motor activity is almost evenly distributed throughout the dark and the light portion of the day, has been described in various lemur genera (Eulemur, Hapalemur) and in the owl monkey Aotus azarai of the Argentinean Chaco. Proximate and ultimate factors responsible for this behaviour are still being debated. However, the chronobiological background of the behaviour has largely been ignored. We studied E. fulvus albifrons and A. a. boliviensis under controlled laboratory conditions to assess whether their activity rhythm is endogenously regulated by a circadian timing system that obeys general rules found in other mammals, or whether there are characteristic differences. To this end, we carried out long-term activity recordings on individuals of both subspecies kept under constant light and various light-dark cycles (LDs) using a PC-controlled electro-acoustic device in combination with telemetric body temperature measurements. Both subspecies developed free-running circadian activity and body temperature rhythms with periods deviating from 24 h in constant light, and LDs turned out to be the most efficient Zeitgeber synchronizing this endogenous rhythmicity to the external 24-hour day. The luminosity prevailing during the dark time of the LD had a decisive effect on levels of activity in the lemurs and induced strong masking effects on their circadian activity pattern. The results indicate that, from a chronobiological viewpoint, both species should be considered as dark active primates. Their diel activity rhythm is regulated by a normally responding circadian timing system and strong activity inhibiting or enhancing direct effects of light intensity. Thus, hypotheses on proximate and/or ultimate factors of cathemerality in primates must also consider its circadian background.